Various embodiments described herein relate generally to the field of heating, ventilation, and air conditioning (HVAC), and more particularly to HVAC systems able to control different zones independently that locally re-circulate air and receive supply of fresh air from a single air-handling unit.
The exhaust systems within zones remove the air to the outside without recirculation. Such an HVAC system will be particularly useful and effective for use in biological and pharmaceutical manufacturing operations where it is critical to prevent cross contamination between zones, control the quality of air within strict ISO standards and maintain an appropriate temperature despite the heat load from the equipment operating within a zone, all at a reduced cost of installation and operation of a HVAC system.
Additionally, such an HVAC system will be useful for hospitals, research laboratories and other such facilities where a structure demands varying requirements of air quality and isolation from other zones.
A conventional forced air variable air volume (VAV) system distributes air to terminal units installed in habitable spaces throughout a building. The air is cooled or heated central equipment zones. The an supplied is called primary or ventilation air.
The primary air is first tempered through a large air-handling unit and then distributed to the rest of the zones through conventional air ductwork. The large air-handling unit may consist of a supply fan, cooling coil, hearing coil, filters, condensate drain pans, outside air dampers, sensors, controls, etc., but not any return air dampers or controls. Once the primary air leaves the air-handling unit the primary air is distributed throughout the zones through air ductwork and then to in-zone terminal units such as air distribution units and terminal units. A single in-zone terminal unit usually conditions a single space, but some (e.g., a large fan-coil unit) may serve several spaces.
Conventional forced air variable air volume systems work well in various manufacturing operations such as in pharmaceutical and biotechnology manufacturing. In most climates, these VAV systems are typically installed to condition perimeter building spaces and are designed to provide all desired space heating and cooling, outside air ventilation, and simultaneous heating and cooling in different parts of the building during intermediate seasons.
A conventional forced air variable air volume system generally serves also as a recirculating unit wherein the air from the various zones of a building is brought back into the unit to conserve the cost of conditioning the air; this cost can be substantial since it involves humidification or dehumidification, temperature control and air filtration. If the air is supplied to ISO controlled areas where clean air is supplied, recirculation becomes inevitable to conserve cost.
Air recycling has one major disadvantage: it mixes the air from various zones and is the major source of cross contamination between and among the zones. A simple but extremely costly solution is to provide a separate air-handling unit for each zone in need of isolating from other zones. This is how the pharmaceutical and biotechnology industry designs its facilities. The challenges become more formidable in the manufacturing of biological products where each step of manufacturing should be ideally isolated from others as the product progresses to a purer form. An example of this situation arises in the purification of recombinant proteins made from mammalian cells where there remains a risk of viral contamination. Each step of purification reduces the viral load and it is critical that the air from earlier steps should not mix with the air in the zones where later processes are executed. The choice of separate air-handling units resolves the problem but adds substantial capital investment and a very high life-time cost of operations.
To minimize energy consumption, the large air-handling units generally recycle the circulated air and only add a small portion of fresh air. Such recycling, however, may result in air borne contaminants and bacteria, being spread throughout the building resulting in “sick building syndrome.” Other disadvantages may include draughts, lack of individual control, increased building height required to accommodate ducting, and noise associated with air velocity. Additionally, for many buildings, the use of in-zone terminal units may be limited to perimeter spaces, with separate systems required for other areas. More controls may be needed as compared to other systems.
In many systems, the primary air is supplied at a constant rate with no provision for shut off, which may be a disadvantage as tenants may prefer to shut off their heating or air conditioning or management may desire to do so to reduce energy consumption. In many systems, low primary chilled water temperature and or deep chilled water coils are required to control space humidity accurately, which may result in more energy consumption from a chiller, cooling tower, and/or pumps. A conventional forced air variable air volume system may not be appropriate for spaces with large exhaust requirements such as labs unless supplementary ventilation is provided. In many systems, low primary air temperatures require heavily insulated ducts. In many systems, the energy consumption is high because of the power needed to deliver primary air against the pressure drop of the terminal units. The initial cost for a VAV system may be high. In many systems, the primary air is cooled, distributed, and may be subsequently re-heated after delivery to a local zone, thus wasting energy. In many systems, individual zone control is expensive as an individual terminal unit or fan coil unit is required for each zone, which may be costly to install and maintain, including for ancillary components such as controls. Moving large flow rates of air thru ductwork is inefficient and wastes energy. Mold and biocides may form in the ductwork and then be blown into the ambient/occupied space.
There remains a need to provide an HVAC system that is capable of providing a low cost solution, both in its design and operation while maintaining a complete isolation of zones and also making it possible to provide a different class of air in each zone; the ideal invention will also allow a separate temperature in each zone and requires very low maintenance.
The present invention discloses a single-pass HVAC systems to isolate zones and to maintain a required clean air quality standard is provided that operates by producing a positive pressure in all zones, while exhausting on a minimal quantity of air required by law. The zones are kept clean by a recirculating fan filter in each zone. The exhaust air is used to exchange heat with incoming air to conserve energy further.